1. Field of the Invention
This invention relates to a tennis practice device, which advantageously damps the oscillatory movement of a tennis ball after it is struck so that such movement occurs within a minimal time before the ball is ready for additional striking. More particularly, it is concerned with a damped tennis practice device having a support, wand structure having a tennis ball mounted on one end thereof, means for connecting the remote end of the wand to the support for pivoting movement of the wand and ball from and to a stationary ready position when the ball is struck, and apparatus for damping the oscillation of the wand after the ball is struck.
2. Description of the Prior Art
Many tennis players wish to practice by themselves, and accordingly many devices have been used in the past for this purpose. Besides conventional return walls found in the vicinity of tennis courts, practice devices for the home or some other convenient location can also be used. These devices typically contain a support, an arm pivotally held on the support for holding a tennis ball, structure for connecting the arm to the support, and some means for damping the oscillatory motion of the arm and ball after the ball is struck. Usually the damping arrangment employs one or more coil springs connected to the arm.
Generally the ball-holding arm is biased toward one particular orientation so that it may be struck repeatedly from one standing position.
The problem with the prior art in this field is that the ball and arm are not generally brought back to the ready position quickly enough. The reason for this problem is most easily seen by dividing the motion of the arm into two phases: (1) an oscillatory phase; and (2) a refractory phase. The oscillatory phase is characterized by one or more pivotal oscillations of the arm about the support, with the biasing, damping and impact forces determining the nature of such motion. The refractory phase begins when the oscillatory motion of the arm has substantially decayed. The refractory motion is characterized by vestigial oscillatory motion of the arm as well as the internal jostlings, rebounds and friction of the arm, ball and support.
The reason that spring damped structures do not adequately solve the problem of returning the arm and ball to a ready static position in a desirable period of time, is because the damping is of a variable nature due to Hooke's law. In other words, the damping force of a spring is proportional to the displacement of the arm from the equilibrium position of the spring. Generally then, as the oscillatory motion decreases, the damping force also decreases. Further compounding this difficulty is the fact that during the refractory period, the arm is relatively close to the equilibrium position of the spring (i.e., the ready position) and consequently there is little or no damping force exerted on the arm or the ball. Hence, motion during the 0 refractory period is only slightly damped if at all.
Patents illustrating these prior devices include U.S. Pat. Nos. 1,826,221, 2,578,313, 2,713,487, 3,051,491, 3,147,979, 3,924,853, 4,089,521, 4,307,888, 4,417,730, 4,531,734, and Australian Patent No. 25,611.